"The evidence is clear: global climate change caused by human activities is occurring now and is a growing threat to society," the AAAS said at its annual meeting.

"Scientists are observing the rapid melting of glaciers, destabilization of major ice sheets, rising sea levels, shifts in species ranges and increased frequency of weather extremes," said John P. Holdren, director of the Woods Hole Research Center and AAAS president.

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Concern focuses on carbon dioxide and other gases produced by burning fossil fuels and other processes. As these gases accumulate in the atmosphere they trap heat from the sun, much like a greenhouse, warming the climate.

"The longer we wait to tackle climate change, the harder and more expensive the task will be," the group said.

Holdren noted that some of the most dramatic changes are occurring in the far North where warming has occurred more rapidly than in other areas. Retreating sea ice and rising sea level are driving some natives from their villages, the group said.

On Feb. 2 the Intergovernmental Panel in Climate Change reported that global warming is so severe that it will "continue for centuries," leading to a far different planet in 100 years.

The panel, established by the United Nations, concluded that global warming is "very likely" caused by man, meaning more than 90 percent certain.

If nothing is done to change current emissions patterns of greenhouse gases, global temperature could increase as much as 11 degrees Fahrenheit by 2100, the report said.

AAAS was founded in 1848. It reports that it serves 262 affiliated societies and academies of science, reaching 10 million individuals.